The invention relates to a pump system of the type included a displacement pump having a two-way pipe, said two-way pipe at one side being coupled, via a first non-return valve, to a supply pipe for sucking a quantity of medium from said supply pipe into said two-way pipe, said two-way pipe likewise being coupled at one side, via a second non-return valve, to a discharge pipe, in order to force a corresponding quantity of medium out of said two-way pipe, said pump system being provided with a curved pipe which is connected to the other side of said two-way pipe and which is coupled to said displacement pump.
Such a pump system is known from DE 30 12 028. The pump system known from said publication is provided with a dividing element disposed in the two-way pipe to the displacement pump, said dividing element being movable within a cylinder. At the side of the dividing element remote from the two-way pipe a working medium, which is stored in a storage vessel, is injected. The quantity of injected working medium is always larger than the losses through leakage along the displacement means. Towards the end of a delivery stroke of the displacement pump the excess working medium formed as a result of said injecting is forced through a gap between the dividing element and the wall of the cylinder, in the direction of the medium to be pumped which is present in the two-way pipe, and which may be hot. As a result of fresh and cool working medium being injected a required low operating temperature of the displacement pump is maintained, and it is prevented that the generally abrasive and hot medium comes into contact with the displacement pump. The disadvantage of the pump system described in the above-mentioned German document is inter alia that a continuous, usually undesirable dilution of the medium to be pumped takes place. A further disadvantage is that it is necessary to provide valves in order to inject fresh working medium, which valves also require regular maintenance. Besides, the storage vessel must regularly be replenished with working medium.
The object of the invention is to provide a pump system, wherein a membrane pump can be utilized for conveying in particular hot mediums, and wherein no working medium needs to be injected into the medium to be pumped at the location where the pump system is installed.
In order to achieve that objective the pump system according to the invention is characterized in that said displacement pump is a membrane pump, and that the pump system has an additional pipe, which is on the one hand connected to the curved pipe and on the other hand to the membrane pump, and that the pump system is provided with heat exchange means provided around said additional pipe.
It is noted here that the term membrane pump must be understood to mean a pump which derives its pumping action from the movement of a hermetically sealed element. The movement of said element which may have the shape of a membrane, a bellows, a hose and the like, may be imparted by means directly coupled to said element, e.g., hydraulically, pneumatically or mechanically moved means, but it may also be done indirectly. By indirect is meant that the movement of a displacement body, e.g., a piston plunger, is transmitted to the hermetically sealed element via an intermediate medium, usually a fluid.
The advantage of the pump system according to the invention is that, in particular because an additional pipe is used, it can be achieved that the hot medium itself does not come near the membrane pump when periodically moving in and out of the two-way pipe, not even if the swept volume of the membrane pump is large. As a result of that the heat which is absorbed from the hot medium by the additional pipe will mainly be conduction heat, as a result of which the heat capacity of the heat exchange means can remain minimal, in spite of the fact that for pumping the hot medium from the supply pipe to the discharge pipe a membrane pump is used that is not resistant to the heat of the medium. In the pump system according to the invention the displacement pump may thus comprise a displacement body made of an elastomeric material.
No separate working medium is required with the pump system according to the invention. When a very hot medium is pumped, a cooling medium may injected near the membrane pump, if required, which medium may readily be a portion separated from the medium to be conveyed itself, in which case said portion must be slightly cooled first. It is not necessary, however, to use a working medium other than the medium to be pumped.
A further advantage of the pump system according to the invention is that because of the slightly elastically deformable angular pipe portion, which comprises the two-way pipe, the curved pipe and the additional pipe, it is possible to allow in particular said angular pipe portion to expand and to shrink when temperature changes occur, so that it is prevented that, when mediums having widely varying temperatures are pumped, high forces are exerted and that deformations occur in the pump system at places where this is undesirable.
One embodiment of the pump system according to the invention is characterized in that the swept volume of the displacement pump is smaller than the internal volume of the two-way pipe.
The advantage of this embodiment of the pump system according to the invention is that the point located closest to the membrane pump and bounding the internal volume of the two-way pipe, which pipe is filled with sucked-in medium each time, the so-called point of reversal, lies within the two-way pipe itself. Accordingly a large amount of heat will be transferred from the hot medium only to the two-way pipe itself, and the additional pipe will not come into direct contact with the hot medium. As a result of this the heat capacity of the heat exchange means may be further reduced, in order to be able to achieve a sufficiently low temperature near the membrane pump.
Preferably the radius of curvature the curved pipe at least equals one and a half times the internal diameter of the curved pipe.
A further embodiment of the pump system according to the invention is characterized in that the additional pipe is disposed substantially vertically.
Because of this it is achieved that the point of reversal remains within the two-way pipe, and does not move through the curved pipe in the direction of the heat exchange means and the membrane pump. As a result of the action of gravity the medium near the membrane pump rather tends to go down and thus drive the point of reversal towards the two-way pipe.
The invention and its further advantages will be further explained with reference to the accompanying drawing, which illustrates a preferred embodiment of a pump system according to the invention.